Rotational rate sensors with vibrating resonators, also referred to as “vibratory-rate gyroscopes,” measure rotational rates directly by sensing forces generated by the vibrating elements in response to rotation of the sensor. Various configurations of vibratory elements have been developed for use in vibratory-rate gyroscopes, including suspended tuning-fork structures, vibrating beams and vibrating rings. These elements are driven on resonance and the motion of the elements in response to rotation is measured to determine the forces on the elements and the rotation of the sensor.
An illustrative vibratory-rate gyroscope having a tuning fork element is taught in U.S. Pat. No. 5,698,784, Vibratory Rate Gyroscope and Methods of Assembly and Operation, issued to Steven P. Hotelling and Brian R. Land, Dec. 16, 1997. The Hotelling-Land gyroscope utilizes two vibratory elements, one to detect motion about each of two different rotational axes. However, not only does this design require the use of two tuning forks, the two tuning forks must operate at different frequencies in order to minimize crosstalk between the units. From a perspective of complexity and compactness, it is desirable to have a gyroscope capable of sensing rotation about two axes that requires only one vibrating element.
One difficulty with vibratory rate sensors arises from the fact that the driven vibratory motion is very large compared to the forces and motion resulting from rotation. Small amounts of mechanical transducer misalignment can result in the large driven motion causing errors in the small signals being sensed on the other axes. These errors are typically corrected mechanically, by adjusting sensors and/or by trimming material from the vibrating elements However, such mechanical trimming and adjustment is time consuming and expensive. It is desirable to provide automatic error correction electronically and to further provide correction that compensates over a wide variation in operating conditions.
It is also desirable to provide a rotational rate sensor that is small, inexpensive to produce, is adaptable to a wide range of applications, and is easily integrated with microelectronics. Such adaptability would preferably include the ability to adjust the bandwidth of the sensor and to provide for uniform output from a number of sensors.
Vibrating sensors are sensitive to vibrations, both external vibrations and self-generated vibrations that can be reflected back into the sensor. It is therefore desirable to isolate the rotational rate gyroscope from such vibrations. Preferably this isolation is done with a simple and effective suspension system having a minimum of components, and not having non-essential wires for communications and power to complicate the isolation function and compromise the longevity of the sensor.
It is further desirable to provide a rotational rate sensor having provision for storing unit-specific calibration values and seed values to speed up the startup settling times
The present invention is directed to providing these advantages.